In an ATM network, a message is transported from a source to a receiver via a virtual circuit. The virtual circuit is activated whenever the source sends a message to the receiver. Such a circuit is established using a so-called connection oriented service that is invoked when the source initially enters a request to send data to the receiver. The ATM switch serving the source responds to the request by first consulting a routing table that identifies an output path that may be used to forward a call set-up message to the ATM switch serving the receiver and then transmitting the message over that path. It can be appreciated that the call set-up message may be processed by one or more intermediate ATM switches before it actually reaches the destination ATM switch. Each ATM switch that receives the call set-up message establishes a virtual connection through its switching fabric to an output path extending to the next switch that will form the virtual connection and sends the call set-up message thereto. The origination ATM switch thereafter activates the established virtual connection when it transmits a cell containing a virtual path identifier and virtual circuit identifier which uniquely identify a segment of the virtual circuit connection extending to either the destination switch or a next intermediate switch.
It can be appreciated from the foregoing that establishing a virtual connection is somewhat cumbersome and is typically done regardless of the amount of data that a source sends to a receiver. That is, a virtual connection is established even when the data that needs to sent to a receiver can fit into a short datagram flow, e.g., a relatively small number of data packets.